Abstract: An experimental investigation has been conducted to ex-plore a novel method for measuring the porosity of core samples,which will not both pollute the core and change the original porosity of the core. The method takes advantage of measuring natural Radon(Rn) from the radioactive decay of radioisotope
Radium in the core sample instead of fluid injection /saturation as in common porosity measurement. Experimental results and theoretical analysis show that the new method can effectively measure the porosity of a core with a certain intensity of natural radioactivity, and has the special advantage for determining the residual fluid saturation of a core after displacement. As the
method would be limited by the content of the natural radioiso-tope in the core sample, measures for further improvement of the method are proposed.

Key words: core, porosity measurement, radioisotope, radioactive equilibrium, Radon, Gamma spectrum